As a conventional displacement type fluid machine, a reciprocating fluid machine for moving a working fluid by repeating a reciprocation of a piston in a cylindrical cylinder, a rotary (rolling piston type) fluid machine for moving the working fluid by eccentrically rotating a cylindrical piston in the cylindrical cylinder, a scroll fluid machine for moving the working fluid by engaging fixed scroll with an orbiting scroll having spiral wraps standing up on end plates and by gyrating the orbiting scroll are well known.
Since the reciprocating fluid machine is simply constructed, it is possible to prepare the machine easily and to be inexpensive. On the other hand, since a process from a suction completion to a discharge completion is short of shaft angle of 180.degree. so that a flow velocity of the process for the discharge gets faster, there is a problem that a pressure loss is increased so that a performance is reduced. Further, since it is necessary to reciprocate the piston, so that a rotary shaft system can not be completely balanced, there is another problem that a vibration and a noise is larger.
Also, in the case of the rotary fluid machine, since the process from the suction completion to the pressure completion has the shaft angle of 360.degree., there is less problem that the pressure loss during the discharge process is increased compared to the reciprocating fluid machine. However, since the working fluid is discharged once per one rotation of the shaft, a variation of a gas compression torque is relatively higher, accordingly, there is the same problem of the vibration and noise as the reciprocating fluid machine.
Further, in the case of the scroll fluid machine, since the process from the suction completion to the discharge completion has the long shaft angle of 360.degree. or more (the scroll fluid machine practically used as an air conditioner has usually 900.degree.), so that the pressure loss during the process of the discharge is low, a plurality of working chambers are formed generally, so that there is an advantage that the variation of the gas compression torque is low and the vibration and noise is less. When the wraps are engaged, it is necessary to manage a clearance between the spiral wraps and the clearance between the end plate and a wrap tip. Thus, the fluid machine must be worked with high accuracy, so that there is further problem that the expense of working is expensive. Further, since the process from the suction completion to the discharge completion has the long shaft angle of 360.degree. or more, it takes a long time for the compression process, so that there is further problem that an internal leakage is increased.
By the way, known is a displacement type fluid machine in which a displacer (a rotary piston) for moving the working fluid is not rotated relative to the cylinder in which the working fluid is suctioned, but is gyrated with an almost constant radius, that is, is gyrated to transmit the working fluid. This kind of displacement type fluid machines have been proposed in Japanese Patent Unexamined Publication No. 55-23353 (Document 1), U.S. Pat. No. 2,112,890 (Document 2), Japanese Patent Unexamined Publication No. 5-202869 (Document 3) and Japanese Patent Unexamined Publication No. 6-280758 (Document 4). These displacement type fluid machines comprise a petal-shaped piston having a plurality of members (vanes) radially extended from a center and a cylinder having a hollow portion having an almost the same shape as this piston, wherein this piston is gyrated in this cylinder in order to move the working fluid.